Protective film for protecting a dielectric layer of a plasma display panel from discharge, method of forming the same, plasma display panel and method of manufacturing the same

ABSTRACT

A protective film for protecting a dielectric layer of a plasma display panel from discharge contains a metallic oxide. A volume resistivity of the protective film is 3.5×10 11  ω·cm or more.

BACKGROUND OF THE INVENTION

[0001] Field of the Invention

[0002] The present invention relates to a protective film for protectinga dielectric layer of a plasma display panel from discharge, a method offorming the same, a plasma display panel and a method of manufacturingthe same, and more particularly, to a protective film of which adischarge characteristic is improved, a method of forming the same, aplasma display panel and a method of manufacturing the same.

[0003] Description of the Related Art

[0004] Generally, a plasma display panel (PDP) has a thin structure, noflicker and a great display contrast ratio. Also, the PDP has a largenumber of features that it can be manufactured as a relatively largescreen, its response speed is fast, a multicolor light emission ispossible by using a fluorescent material because it is a spontaneouslight emission type, and the like. Therefore, recently, the PDP has beenwidely used for the display device field related to the computer and thecolor image display field.

[0005] In the plasma display according to an operating method, there areAC driving type where electrodes are coated with a dielectric andoperated indirectly in AC discharge state and DC driving type whereelectrodes are exposed to a discharge space and operated in DC dischargestate. Further, in the AC driving type plasma display, there are amemory operating type to use memory of discharge cell as a drivingmethod and a refresh operating type not to use it. And, brightness ofthe AC driving type plasma display is proportional to the number ofdischarge times. In case of the above refresh operating type, it ismainly used in the plasma display having small display capacity becausebrightness decreases when display capacity increases.

[0006]FIG. 1 is an exploded view schematically showing a structure ofthe AC driving memory operating type color plasma display.

[0007] In PDP, two isolation substrates 101 and 102 made of grass areprovided. The isolation substrate 101 becomes a rear substrate, and theisolation substrate 102 becomes a front substrate.

[0008] On the isolation substrate 102, transparent electrodes 103 and104 are provided on a face side opposite to the isolation substrate 101.The transparent electrodes 103 and 104 are extended in a horizontaldirection (transverse direction) of the panel. Also, trace electrodes105 and 106 are arranged to overlap the transparent electrodes 103 and104, respectively. The trace electrodes 105 and 106 are made of, forexample, metal material and provided in order to lower electroderesistance value between each electrode and external driving device.Further, there are formed a dielectric layer 112 covering thetransparent electrodes 103 and 104, a plurality of black stripe layers108 formed on the dielectric layer 112 and extended in a verticaldirection (longitudinal direction) of the panel, color filter layers110R, 110G and 110B of red color R, green color G and blue color Bformed between the black stripe layers 108, and a protective film 114for protecting the dielectric layer 112 and the transparent electrode103 from discharge.

[0009] Also, because PDP emits each visible light of R, G and B byexciting the fluorescent material with emitted ultraviolet light, thecolor filter layers are not necessarily needed. The color filter layersare to collect spectrum of luminescent colors by the fluorescentmaterial.

[0010] On the isolation substrate 101, data electrodes 107 perpendicularto the transparent electrodes 103 and 104 are provided on a face sideopposite to the isolation substrate 102. Therefore, the data electrodes107 are extended in the vertical direction. Further, a partition wall109 is provided to divide a display cell in the horizontal direction.The partition wall 109 is opposite to the black stripe layers 108.Further, a dielectric layer 113 covering the data electrodes 107 isformed, and a fluorescent layer 111 to transform ultraviolet lightgenerated by discharging of discharge gas into visible light is formedon a side surface of the partition wall 109 and a surface of thedielectric layer 113. Further, a discharge gas space is secured by meansof the partition wall 109 in the space between the isolation substrates101 and 102, and the discharge gas space is filled with a discharge gasconsisting of helium, neon, xenon or mixture of gases thereof.

[0011] The protective film 114 is provided in order to protect thedielectric layer 112, the transparent electrode 103 and the like. fromsputtering by ion bombardment during discharge as mentioned above, andbecause the protective film 114 comes in contact with the discharge gasspace, its material and film quality affect greatly the dischargecharacteristic. Further, in AC driving type PDP, low consuming power,simplification of driving circuit, high precision and larger screen areimportant factors.

[0012] Therefore, generally, magnesium oxide MgO is used as a materialof the protective film 114. MgO is an insulator having excellentsputtering resistance and a large secondary electron emissioncoefficient. The driving of PDP becomes possible with lowering dischargestarting voltage by using MgO.

[0013] Subsequently, a conventional method of forming the protectivefilm in the PDP will be described. The protective film is generallyformed by a vacuum deposition method. FIG. 2 is a schematic diagramshowing a conventional film forming apparatus of the protective film.

[0014] In the conventional film forming apparatus, a deposition chamber121 is provided. In an upper part of the deposition chamber 121, asubstrate 124 in which a dielectric layer, etc. have already been formedand MgO film is formed is mounted. Also, in lower part of the depositionchamber 121, a deposition source 125 composed of MgO as a raw materialof the protective film is mounted. Further, in the deposition chamber121, a heater 132 heating the substrate 124 and a gas inlet (not shown)for O₂ gas are formed.

[0015] In case of manufacturing the protective film using theconventional film forming apparatus configured as mentioned above,first, the substrate 124 is fixed in the upper part of the depositionchamber 121, and the substrate 124 is heated by the heater 132, andsimultaneously, the deposition chamber 121 is exhausted. Subsequently,in order to arrange crystal orientation of MgO film, while oxygen gas isintroduced into the deposition chamber 121, an electron beam 133 isirradiated to the deposition source 125 so that the MgO film is formedas the protective film on the opposite side to the deposition source 125of the substrate 124.

[0016] Further, in order to improving an orientation property of the MgOfilm, the method of forming the MgO film in an atmosphere includinghydrogen atom in excited or ionized state is disclosed (Japanese PatentLaid-Open No. Hei 9-295894 Publication).

[0017] Further, in order to lower a discharge voltage by improving thesecondary electron emission coefficient of the protective film, the PDPin which an orientation of the protective film is in (n00) or (mm0)orientation and a surface roughness is 30 nm or more is disclosed(Japanese Patent Laid-Open No. Hei 11-3665 Publication).

[0018] However, in the display operation of the conventional AC memoryoperating type PDP, first, a discharge is generated in a discharge spaceby applying a discharge voltage pulse to the transparent electrodes 103and 104. By this discharge, on the surface of the discharge space sideof the protective film 114, a charge having opposite polarity to thepolarities applied to each electrode is accumulated at the positionwhere the transparent electrodes 103 and 104 face each other (wallcharge forming step).

[0019] Then, a discharge is generated once more in the discharge spaceby applying a voltage having opposite polarity to the above dischargevoltage pulse to the transparent electrodes 103 and 104. The accumulatedcharge (wall charge) is erased by this discharge so that the wall chargedoes not exist in the entire surface of PDP (erasing step of wall chargeor erasing step).

[0020] Subsequently, the transparent electrode 103 is scanned byapplying a predetermined voltage in turn, and a wall charge isaccumulated as a preparation for displaying a light emitting cell byapplying a predetermined voltage between the transparent electrode 103in the voltage applying state and the data electrode 107 correspondingto a light emitting cell to be displayed out of the light emitting cellsbelonging to the transparent electrode 103 (writing step).

[0021] Next, an image display is performed by applying a sustainingdischarge pulse voltage to the transparent electrodes 103 and 104 on theentire surface of PDP. And, because the voltage value of the sustainingdischarge pulse voltage is set to be lower than that of discharge pulsevoltage light emission is not generated, light emission does not occurin a light emitting cell in which the wall charge is not formed in thewriting step, and light emission occurs only in a light emitting cell inwhich writing discharge is performed so that the image display isperformed (display discharge step). In a gradation display, about 256level display gradations are accomplished by combining in time seriesabout eight kinds of sustaining discharge pulse groups of which thenumber of pulses is different according to the number of gradations(subfield gradation method).

[0022]FIGS. 3A and 3B are graphs showing the relationship between theapplying voltage and discharge delay light emission in which an abscissaindicates the time and an ordinate indicates the light emissionintensity and voltage. In the PDP, in case where there is no dischargedelay, namely, light emission delay, because a discharge is startedalmost simultaneously in response to writing pulse applying start asshown in FIG. 3A, the light emission intensity characteristic having avery sharp peak is obtained. However, in case where there is dischargedelay in each light emitting cell according to the secondary electronemission efficiency, each light emitting cell starts the dischargeindividually in response to the writing pulse applying start. Therefore,the peak of light emission intensity is lower and its width becomeswider than comparing with the case where there is no discharge delay, asshown in FIG. 3B. Further, all the light emitting cells do not startdischarge simultaneously within the writing pulse applying time.Therefore, the light emitting cells in which writing is not stillcompleted remain at the point of the writing pulse applying expirationtime. Further, a portion indicated by a broken line in FIG. 3B shows anexample of light emission intensity in case where the writing pulse isapplied longer than the shown writing pulse period, and shows that thelight emitting cells to be discharged cannot be discharged duringapplying the writing pulse, namely, the writing operating becomesincomplete. In this case, when the discharge delay is observed as lightemission of the light emitting cell in the entire surface of the PDP, itis observed as flicker of screen display. Therefore, in case where thesecondary electron emission efficiency of the protective film 114 (MgOfilm) is degraded, as shown in FIG. 3B, because the writing pulseapplying time is shortened according to high precision and highgradation of the PDP, there is a problem that the discharge delay andwriting operation becomes incomplete.

[0023] However, when the protective film formed by the conventional filmforming method using the film forming apparatus shown in FIG. 2 is used,the forming time of writing discharge becomes longer so that writingbadness that the discharge is not started within the defined time iseasily occurred. Particularly, the discharge delay is long in thedisplay cell, which becomes an isolation point in time and space, and inthis case, a writing scan pulse width needs to be set longer. However,when the scan pulse width is set longer, there are problems that thenumber of sustaining pulses required for improving brightness isrestricted and the driving by a dual scan to scan upper half part andlower half part of a screen individually is needed. In case of the dualscan, since the number of driving circuits is numerous comparing with asingle scan, it is an obstacle to cut down cost. Further, since acrystal grain diameter is small in the conventional film forming method,there is a problem that the discharge starting voltage is high.

[0024] Further, in the film forming method described in Japanese PatentLaid-Open No. Hei 9-295894 Publication, the orientation property isimproved, but orientation plane is not uniform. Therefore, there aresome cases where sputtering resistance becomes insufficient. Further,the crystal grain diameter becomes small, and the discharge startingvoltage becomes high. Similarly, in the PDP described in Japanese PatentLaid-Open No. Hei 11-3665 Publication, the sputtering resistance as aprotective film is insufficient.

SUMMARY OF THE INVENTION

[0025] An object of the present invention is to provide a protectivefilm for protecting a dielectric layer of a plasma display panel fromdischarge by which luminance can be improved, writing badness can bereduced and the number of driving circuits can be decreased by means ofsecuring sufficient sputtering resistance and shortening a dischargedelay time, a method of forming the same, a plasma display panel and amethod of manufacturing the same.

[0026] According to one aspect of the present invention, a protectivefilm protecting a dielectric layer of a plasma display panel fromdischarge contains metallic oxide. A volume resistivity of saidprotective film is 3.5×10¹¹ Ω·cm or more.

[0027] The protective film may contain 3 hydrogen atoms or more when thenumber of total atoms in the protective film is defined as 100.

[0028] According to another aspect of the present invention, aprotective film protecting a dielectric layer of a plasma display panelfrom discharge contains metallic oxide and hydrogen. The number ofhydrogen atoms is 3 or more when the number of total atoms in theprotective film is defined as 100.

[0029] In the present invention, the volume resistivity and/or thehydrogen atom content of the protective film are defined. The inventorsof the present invention found that the volume resistivity and hydrogenatom content are closely related to the discharge delay time of writingand discharge voltage in the PDP, and with defining them in anappropriate range, shortening of discharge delay time, lowering ofdischarge voltage and improvement of brightness are attained.

[0030] The metallic oxide may be MgO. A peak of light emission intensityof light emitting center in 510 to 560 nm in a cathode luminescence maybe higher than that of light emission intensity of light emitting centerin 280 to 440 nm or 680 to 760 nm. Further, the number of the hydrogenatoms may be at least the number of total deficits of total oxygen atomsand metal atoms. The protective film may be formed by means ofperforming a heat treatment in atmosphere including hydrogen in excitedor ionized state. A surface roughness Ra of the protective film may be 5nm or more. It is preferable that the protective film has (111)orientation. In case where a protective film shows (111) orientation,high sputtering resistance can be obtained.

[0031] According to another aspect of the present invention, a method offorming a protective film protecting a dielectric layer of a plasmadisplay panel from discharge, comprises the steps of: forming a metallicoxide film; and performing a heat treatment of said metallic oxide filmin atmosphere including hydrogen in excited or ionized state.

[0032] According to another aspect of the present invention, a method offorming a protective film protecting a dielectric layer of a plasmadisplay panel from discharge, comprises the step of forming a filmcontaining a metallic oxide while performing a heat treatment inatmosphere including hydrogen in excited or ionized state.

[0033] According to another aspect of the present invention, a method ofmanufacturing a plasma display panel, comprises the step of forming aprotective film by the above-described method.

[0034] According to the present invention, since the volume resistivityand the hydrogen atom content closely related to the discharge delaytime of writing and the discharge voltage, etc. in the PDP are properlydefined, the discharge delay time can be shortened. As a result, theluminance can be improved, the writing badness can be prevented, andsimultaneously, the number of driving circuits can be reduced, and thecost can be lowered. Further, consuming power can be reduced by means oflowering the driving voltage (discharge voltage).

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIG. 1 is an exploded view schematically showing a structure ofthe AC driving memory operating type color plasma display;

[0036]FIG. 2 is a schematic diagram showing the conventional filmforming apparatus of protective film;

[0037]FIG. 3A and FIG. 3B are graphs showing the relationship betweenthe applying voltage and the discharge delay light emission in which anabscissa indicates is the time and an ordinate indicates the lightemission intensity and voltage;

[0038]FIG. 4 is a graph showing the relationship between the volumeresistivity and the discharge delay time;

[0039]FIG. 5A is a timing chart showing the applying pulse, and FIG. 5Bis a schematic diagram showing the light emitting spectrum obtained bydischarge;

[0040]FIG. 6 is a schematic diagram showing the discharging part inmeasuring discharge delay time;

[0041]FIG. 7 is a graph showing the relationship between the lightemitting wavelength and light emission intensity by the cathodeluminescence in the samples of which discharge delay time is different;

[0042]FIG. 8 is a schematic diagram showing a first film formingapparatus used in manufacturing a protective film;

[0043]FIG. 9 is a schematic diagram showing a second film formingapparatus used in manufacturing a protective film;

[0044]FIG. 10 is a schematic diagram showing a third film formingapparatus used in manufacturing a protective film;

[0045]FIG. 11 is a graph showing the relationship between the hydrogencontent and the discharge delay time;

[0046]FIG. 12 is a graph showing the relationship between the hydrogencontent and the priming voltage;

[0047]FIG. 13 is a graph showing the spectrums of H atom and Mg atom incase where the partial pressure ratio of hydrogen and oxygen is 0.5 inan atmosphere within the chamber;

[0048]FIG. 14 is a graph showing the spectrums of H atom and Mg atom incase where the partial pressure ratio of hydrogen and oxygen is 0.2 inthe atmosphere within the chamber;

[0049]FIG. 15 is a microphotograph showing the surface shape of theprotective film in case where the partial pressure ratio of hydrogen andoxygen is 0.5 in the atmosphere within the chamber;

[0050]FIG. 16 is a microphotograph showing the surface shape of theprotective film in case where the partial pressure ratio of hydrogen andoxygen is 0.2 in the atmosphere within the chamber;

[0051]FIG. 17 shows the result of X-ray diffraction in case where thepartial pressure ratio of hydrogen and oxygen is 0.5 in the atmospherewithin the chamber; and

[0052]FIG. 18 shows the result of X-ray diffraction in case where thepartial pressure ratio of hydrogen and oxygen is 0.2 in the atmospherewithin the chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] As a result of repeating experimental study in order to solve theabove-mentioned problems, the inventors of the present invention foundthat the discharge delay time can be shortened by means of defining avolume resistivity or a hydrogen content of a protective film in apredetermined range. Further, when an orientation of the protective filmis (111) orientation, the best sputtering resistance can beaccomplished.

[0054] Hereinafter, a protective film according to the present inventionwill be described in detail. First, the volume resistivity and thehydrogen content of the protective film will be explained.

[0055] Volume resistivity: 3.5×10^(11 Ω·cm or more)

[0056] As a result of study on the relationship between the volumeresistivity and the discharge delay time conducted by the inventors ofthe present invention, the following relationship was found. FIG. 4 is agraph showing the relationship between the both in which an abscissaindicates the volume resistivity and an ordinate indicates the dischargedelay time.

[0057] As shown in FIG. 4, as the volume resistivity is increased, thedischarge delay time is shortened. The discharge delay time depends on adriving method and a shape of a discharge cell of PDP. Also, anallowable range of the discharge delay time depends on the number ofscan lines and a driving method. In the PDP used when obtaining thegraph shown in FIG. 4, when the discharge delay time becomes about 4 μsor more, the writing discharge is not generated within the applying timeof the writing pulse so that flicker is generated by the writingbadness. Further, because the scan pulse width needs to be set longer,the number of sustaining pulses is restricted so that it is difficult toobtain sufficient luminance. However, in case where the discharge delaytime is not more than 4 μs, sufficient luminance can be obtained becausethe scan pulse corresponding to the width as much as restricting thenumber of sustaining pulses is not needed. Further, in case where thedischarge delay time is not more than 1.8 μs, the number of drivingcircuits can be reduced because it is possible to secure the sufficientscan period by the single scan.

[0058] In measuring the discharge delay time, a PDP was actuallyassembled, and the discharge delay time was measured every 10 displaycells lengthwise and crosswise as an isolation point which is notaffected by discharge in other adjacent display cell. FIG. 5A is atiming chart showing the applying pulse, FIG. 5B is a schematic diagramshowing the light emitting spectrum obtained by discharge, and FIG. 6 isa schematic diagram showing the discharge place in measuring dischargedelay time. The discharge was simultaneously generated in display cells5 indicated by hatching in FIG. 6.

[0059] As shown in FIG. 5A, when generating the discharge, a pulse of−195V was applied to a scanning electrode, a voltage of 70V was appliedto a data electrode, and the above-described experiment was performed2000 times with respect to one display cell. As a result, as shown inFIG. 5B, some discrepancies occur in the light emitting spectrums, butin this measurement, the discharge delay time was defined as the timefrom the pulse applying time to the time when the light emittingspectrum is decreased to 10% of the peak value in the discharge whichreached the peak value lastly.

[0060] The above-mentioned tendency obtained by such measurement methodis not changed although the driving method, the shape of discharge cellor the like is changed. However, the numerical value of the dischargedelay time is different according to the driving method and the shape ofdischarge cell.

[0061] Accordingly, the volume resistivity of the protective film isdefined as 3.5×10^(11 Ω·cm or more.)

[0062] Further, the discharge delay is composed of the sum of astatistical delay and a forming delay from a viewpoint of the dischargephenomenon. Out of the statistical delay and the forming delay, thedelay changed by the volume resistivity of MgO is only the statisticaldelay. Accordingly, even in case where the statistical delay time isshortened by increase of the volume resistivity, the discharge delaytime becomes gradually close to the forming delay time and saturated. Inthe PDP used when obtaining the graph shown in FIG. 4, because theforming delay time was about 1 μs, it is supposed from FIG. 4 that thestatistical delay time became about 0 μs when the volume resistivitybecame 0.4×10¹² Ω·cm. However, the statistical delay time is changed,for example, by the applying voltage besides the volume resistivity. Inother words, in case where the applying voltage is lowered, thestatistical delay time is increased. Accordingly, it is preferable thatthe volume resistivity is 0.4×10¹² Ω·cm or more in order to be able todrive by the even lower applying voltage.

[0063] Also, as a result of study on the relationship between the lightemitting center and the discharge delay time by measuring the cathodeluminescence of MgO film conducted by the inventors of the presentinvention, the following relationship was found. FIG. 7 is a graphshowing the relationship between the both in which an abscissa indicatesthe light emitting wavelength and an ordinate indicates the lightemission intensity. Further, in FIG. 7, a solid line indicates the lightemission intensity in PDP where the discharge delay time is 1.2 μs, abroken line indicates the light emission intensity in PDP where thedischarge delay time is 2.0 μs, and a dashed chain line indicates thelight emission intensity in PDP where the discharge delay time is 3.0μs. The light emission intensity has significance in the relative valuein each curved line, and the absolute value has no particular meaning.

[0064] As shown in FIG. 7, in PDP where the discharge delay time is 1.2μs (the solid line), the peak of the light emission intensity appears atonly the light emitting wavelength of about 520 nm.

[0065] Meanwhile, in PDP where the discharge delay time is 2.0 μs (thebroken line), the peak of the light emission intensity appears at thelight emitting wavelengths of about 520 nm and 360 nm, and the peak isgreater at the light emitting wavelength of about 360 nm.

[0066] Further, in PDP where the discharge delay time is 3.0 μs (thedashed chain line), the peak of the light emission intensity appears atthe light emitting wavelengths of about 400 nm and 730 nm, and the peakis greater at the light emitting wavelength of about 400 nm.

[0067] According to the literature “M. 0. Aboelfotoh: Binn. Display Res.Conf. Records. P62 (1978)”, it is described that an absorptionwavelength peak at the light emitting wavelength of 360 nm to 400 nm isa peak called F+ center caused by oxygen deficit, an absorption peak atthe light emitting wavelength of about 520 nm is a peak caused byexciton, and an absorption peak at the light emitting wavelength ofabout 730 nm is a peak caused by excessive oxygen.

[0068] Therefore, it is thought that in the panel where the dischargedelay time is short, defect caused by oxygen deficit and excessiveoxygen is decreased. From this result, it is preferable that in thecathode luminescence, the peak of light emission intensity of lightemitting center in 510 to 560 nm is higher than that of light emissionintensity of light emitting center in 280 to 440 nm or 680 to 760 nm. Atthis time, it is thought that the number of hydrogen atoms in theprotective film is included not less than the number of total deficitsof oxygen atom and metal atom in the protective film.

[0069] Further, the cathode luminescence is an analysis method ofobtaining information on the defect and the like of a sample bydetecting the light emission as an energy relief process when anelectron beam was irradiated to the sample. In the cathode luminescenceherein, a PDP was assembled once, and the discharge delay time wasmeasured by the above method, and then, the PDP was disassembled, andthe electron beam was directly irradiated to the protective film,thereby detecting the light emission.

[0070] Next, the method of manufacturing the protective film includingthe above-mentioned volume resistivity will be described. FIG. 8 is aschematic diagram showing a first film forming apparatus used inmanufacturing the protective film.

[0071] In the first film forming apparatus, a deposition chamber 11 anda hydrogen treatment chamber 12 partitioned by a gate valve 13 areprovided.

[0072] In an upper part of the deposition chamber 11, a substrate 14 ato which a dielectric layer and the like have been already formed andMgO film is to be formed is mounted. In a lower part of the depositionchamber 11, a deposition source 15 composed of MgO as a raw material ofthe protective film is mounted. Further, in the deposition chamber 11, aheater 22 heating the substrate 14 a and a gas inlet (not shown) for O₂gas are provided.

[0073] Meanwhile, in an upper part of the hydrogen treatment chamber 12,a substrate 14 b to which an MgO film has been formed is mounted. In thehydrogen treatment chamber 12, a heater 16 heating the substrate 14 band a heater 17 heating the inside of the chamber 12 are provided. In alower part of the hydrogen treatment chamber 12, electrodes 18 and 19connected to an external high frequency power supply (RF) 20 arearranged, and a discharge 21 is generated between the electrodes 18 and19. Further, in the hydrogen treatment chamber 12, a gas inlet (notshown) for Ar gas and H₂ gas is provided.

[0074] In case of manufacturing a protective film using the first filmforming apparatus configured as mentioned above, first, the substrate 14a is fixed in the upper part of the deposition chamber 11. Subsequently,the substrate 14 a is heated, for example, at 230 to 270° C. by theheater 22, and at the same time, the deposition chamber 11 is exhausteduntil a degree of vacuum reaches about 8×10⁻⁴ Pa. Next, in order toarrange the crystal orientation of MgO film, while the oxygen gas isintroduced into the deposition chamber 11 at the flow rate of 30 to 80ml/min. (standard state), an electron beam 23 is irradiated to thedeposition source 15 so that MgO film of 5000 to 10000 Å is formed on aface opposite to the deposition source 15 of the substrate 14 a. Also,the substrate 14 b to which an MgO film has been formed is moved intothe hydrogen treatment chamber 12 by opening the gate valve 13.

[0075] Subsequently, in the hydrogen treatment chamber 12, the substrate14 b and inside of the hydrogen treatment chamber 12 are heated, forexample, at 230 to 270° C. by the heaters 16 and 17, respectively.Further, the hydrogen chamber 12 is exhausted until the degree of vacuumbecomes about 5×10⁻⁴ to 9×10 ⁻⁴ Pa, and after the degree of vacuumreaches about 5×10⁻⁴ to 9×10 ⁻⁴ Pa, Ar gas is introduced withcontrolling pressure such that the degree of vacuum becomes about2.1×10⁻¹ Pa. Subsequently, while hydrogen gas is introduced at the flowrate of 30 to 80 ml/min. (standard state), the discharge 21 is generatedin the hydrogen treatment chamber 12 with applying the high frequencyof, for example, 13.56 MHz to the electrodes 18 and 19 by means of thehigh frequency power supply 20. And, a plasma is generated by means ofexciting the hydrogen atom by the discharge 21, and the MgO film formedon the substrate 14 b is exposed to the excited hydrogen, for example,for 8 to 12 minutes to perform the hydrogen treatment of the MgO film.

[0076]FIG. 9 is a schematic diagram showing a second film formingapparatus used in manufacturing the protective film.

[0077] Even in the second film forming apparatus, a deposition chamber11 and a hydrogen treatment chamber 12 a partitioned by the gate valve13 are provided. Because a structure of the deposition chamber 11 is thesame as that of the first film forming apparatus, the detailedexplanation thereof will be omitted.

[0078] In the hydrogen treatment chamber 12 a, a hydrogen ion generatoris provided instead of a plasma generator such as the high frequencypower supply 20. Specifically, an ion gun 26 irradiating ions toward thesubstrate 14 b is provided in the hydrogen treatment chamber 12 a. Theion gun 26 is connected to a hydrogen cylinder 25 through Mass FlowController (MFC) 24 provided in the outside of the hydrogen treatmentchamber 12 a.

[0079] In case of manufacturing the protective film using the secondfilm forming apparatus configured as mentioned above, an MgO film isformed by the same method as the case using the first film formingapparatus, and the substrate 14 b to which the MgO film has been formedis moved into the hydrogen treatment chamber 12.

[0080] Subsequently, in the hydrogen treatment chamber 12, the substrate14 b and the inside of the hydrogen treatment chamber 12 are heated, forexample, at 230 to 270° C. by the heaters 16 and 17, respectively.

[0081] Further, the hydrogen treatment chamber 12 is exhausted, andafter the degree of vacuum reaches 8×10⁻⁴ Pa, hydrogen ion from the iongun 26 is irradiated to the MgO film formed on the substrate 14 b toperform the hydrogen treatment of the MgO film. The flow rate of thehydrogen is defined as 20 to 100 ml/min.

[0082]FIG. 10 is a schematic diagram showing a third film formingapparatus used in manufacturing the protective film.

[0083] The third film forming apparatus has a structure in which thehydrogen treatment chamber 12 a seems to be integrated with thedeposition chamber 11 in the second film forming apparatus.

[0084] Namely, the hydrogen treatment chamber 12 a is not provided, andthe heater 17 and the ion gun 26 are provided in the deposition chamber11.

[0085] In case of manufacturing the protective film using the third filmforming apparatus configured as mentioned above, the substrate 14 a andthe inside of the deposition chamber 11 are heated, for example, at 200to 270° C. by the heaters 22 and 17, respectively, the degree of vacuumis set to 2.7×10⁻² Pa, oxygen gas and hydrogen gas are introduced at theflow rate of 35 to 70 ml/min. (standard state) and 10 to 30 ml/min.(standard state), respectively, and the electron beam 23 is irradiatedto the deposition source 15, thereby forming a MgO film at the rate of80 Å/sec. Further, at the same time, hydrogen ion is irradiated to theMgO film to be formed on the substrate 14 b by means of the ion gun 26to perform the hydrogen treatment of the MgO film. At this time, theflow rate of the hydrogen may be 20 to 100 ml/min.

[0086] Hydrogen content: 3 or more atoms when the number of total atomsof the protective film is defined as 100

[0087] As a result of study on the relationship between the hydrogencontent and the discharge delay time conducted by the inventors of thepresent invention, the following relationship was found. FIG. 11 is agraph showing the relationship between the both in which an abscissaindicates the hydrogen content (the number of hydrogen atoms when thenumber of total atoms of the protective film is defined as 100) and anordinate indicates the discharge delay time.

[0088] As shown in FIG. 11, as the hydrogen content is increased, thedischarge delay time is shortened. As mentioned above, the dischargedelay time depends on the driving method of PDP, the shape of dischargecell and the like. Further, an allowable range of the discharge delaytime depends on the number of scan lines and the driving method. In thePDP used when obtaining the graph shown in FIG. 11, when the dischargedelay time becomes about 1.8 μs or more, the dual scan of PDP isrequired for securing the scan period. Further, since the scan pulsewidth needs to be set longer, the number of sustaining pulses isrestricted so that it is difficult to obtain sufficient luminance. Inthis regard, when the discharge delay time is less than 1.8 sec., thenumber of driving circuits can be decreased because it is possible tosecure the sufficient scan period by the single scan. Further, becausethe scan pulse corresponding to the width as much as restricting thenumber of sustaining pulses is not needed, sufficient liminance can beobtained.

[0089] Further, the inventors of the present invention found thefollowing relationship with respect to the relationship between thehydrogen content and the priming completion voltage. FIG. 12 is a graphshowing the relationship between the both in which an abscissa indicatesthe hydrogen content (the number of hydrogen atoms when the number oftotal atoms of the protective film is defined as 100) and an ordinateindicates the priming completion voltage. The priming completion voltageherein means the lowest voltage that the priming voltage is uniformlyformed in the PDP display plane without generating the writing badnessand the error lighting. The lower the priming setting voltage is, themore the display contrast is improved, but when the priming settingvoltage becomes close to the completion voltage, the writing badness andthe error lighting are easily occurred. Accordingly, 20 to 50V highervoltage than the conventional priming completion voltage is set for thepriming setting voltage. Practically, in the PDP used when obtaining thegraph shown in FIG. 11, when the priming completion voltage is 180V ormore and the priming voltage is not more than 200V, incidence rate ofthe writing badness and the error lighting was increased.

[0090] The priming setting voltage used when obtaining the graph shownin FIG. 11 is measured by setting 20 to 50V higher voltage than thepriming completion voltage. As such, in case where the priming settingvoltage is set with an enough margin with respect to the primingcompletion voltage, the discharge delay time does not depend on thepriming setting voltage.

[0091] Such a tendency is not changed although the driving method or theshape of discharge cell is changed.

[0092] Accordingly, the hydrogen content is defined as 3 atoms or morewhen the number of total atoms of the protective film is defined as 100.

[0093] However, when the hydrogen content exceeds 10 atoms when thenumber of total atoms of the protective film is defined as 100, thedefect in the protective film and the magnesium hydroxide content may beincreased. Therefore, the sputtering resistance as the protective filmis degraded. Thus, it is preferable that the hydrogen content is notmore than 10 atoms when the number of total atoms of the protective filmis defined as 100.

[0094] Further, as a result of study on the relationship of thedischarge delay time and the discharge voltage, and the surfaceroughness Ra conducted by the inventors of the present invention, it wasfound that when the surface roughness Ra is 5 nm or more, the dischargedelay time is shortened, and simultaneously, the discharge voltage islowered because an electric field effectively applied to the surface ofthe protective film is remarkably increased. Accordingly, it ispreferable that the surface roughness Ra of the protective film is 5 nmor more.

[0095] Next, the method of manufacturing the protective film having theabove-mentioned hydrogen content and the surface roughness will beexplained.

[0096] Such a protective film can be manufactured using, for example,the conventional film forming apparatus shown in FIG. 2 or theabove-described first through third film forming apparatus. Forinstance, when the protective film having 5000 to 15000 Å is formed withmaking the pressure within the chamber 2.0×10⁻² to 4.0×10⁻² Pa, thepartial pressure ratio of hydrogen and oxygen 0.3 to 1 in the atmospherewithin the chamber, the substrate temperature 150 to 250° C. and thedeposition rate 1000 to 2000 Å/min., the hydrogen content of theprotective film becomes 3 to 10 atoms when the number of total atoms ofthe protective film is defined as 100, and the surface roughness Rathereof becomes 5 nm or more.

[0097] Under the condition such as the above-mentioned pressure in thechamber, in order to examine the influence on the hydrogen content bychanging only the partial pressure ratio of hydrogen and oxygen, asignal height was measured by ERDA (Elastic Recoil Detection Analysis)method with respect to the number of H atoms which exist in theprotective film, and a signal height was measured by RBS (RutherfordBack-scattering Spectrum) method with respect to the number of Mg atomsand 0 atoms. The detection angle is inclined to the axis of the incidentbeam by 140° in the RBS method, and the detection angle is inclined tothe axis of the incident beam by 20° in the ERDA method. Similarly, inorder to examine the influence on the surface roughness Ra of theprotective film by changing the ratio of the number of hydrogen atomswith respect to the number of oxygen atoms, the surface roughness Ra wasmeasured by using AFM (Atomic Force Microscopy).

[0098]FIG. 13A is a graph showing the spectrum of H atom in case wherethe partial pressure ratio of hydrogen and oxygen is 0.5 in theatmosphere within the chamber, and FIG. 13B is a graph showing thespectrum of Mg atom in case where the partial pressure ratio of hydrogenand oxygen is 0.5 in the atmosphere within the chamber. FIG. 14A is agraph showing the spectrum of H atom in case where the partial pressureratio of hydrogen and oxygen is 0.2 in the atmosphere within thechamber, and FIG. 14B is a graph showing the spectrum of Mg atom in casewhere the partial pressure ratio of hydrogen and oxygen is 0.2 in theatmosphere within the chamber.

[0099] In case where the partial pressure ratio of hydrogen and oxygenis 0.5, as shown in FIG. 13A and FIG. 13B, the signal height of H atombecame 39, and the signal height of Mg atom became 2810. Accordingly, inthe number of atoms in this case, the H/Mg ratio in the protective filmbecomes 0.13. Meanwhile, in case where the partial pressure ratio ofhydrogen and oxygen is 0.2, as shown in FIG. 14A and FIG. 14B, thesignal height of H atom became 19, and the signal height of Mg atombecame 3190. Accordingly, in the number of atoms in this case, the H/Mgratio in the protective film becomes 0.05.

[0100] Further, according to the results separately measured by the RBSmethod, in case where the partial pressure ratio of hydrogen and oxygenis 0.5, the O/Mg ratio in the protective film was 1.20 in the number ofatoms, and in case where the partial pressure ratio of hydrogen andoxygen is 0.2, the O/Mg ratio in the protective film was 1.02 in thenumber of atoms.

[0101] From these results, in case where the partial pressure ratio ofhydrogen and oxygen is 0.5, the hydrogen content of the protective filmbecomes 5.6 when the number of total atoms of the protective film isdefined as 100, and in case where the partial pressure ratio of hydrogenand oxygen is 0.2, the hydrogen content thereof becomes 2.4.

[0102]FIG. 15 is a microphotograph showing the surface shape of theprotective film in case where the partial pressure ratio of hydrogen andoxygen is 0.5 in the atmosphere within the chamber, and FIG. 16 is amicrophotograph showing the surface shape of the protective film in casewhere the partial pressure ratio of hydrogen and oxygen is 0.2 in theatmosphere within the chamber.

[0103] As a result of measuring the surface roughness Ra of theprotective film by using the atomic force microscopy, in case where thepartial pressure ratio of hydrogen and oxygen is 0.5 in the atmospherewithin the chamber, Ra was 5.43 nm, and in case where the partialpressure ratio of hydrogen and oxygen was 0.2 in the atmosphere withinthe chamber, Ra was 4.97 nm.

[0104]FIG. 17 shows the result of X-ray diffraction in case where thepartial pressure ratio of hydrogen and oxygen is 0.5 in the atmospherewithin the chamber, and FIG. 18 shows the result of X-ray diffraction incase where the partial pressure ratio of hydrogen and oxygen is 0.2 inthe atmosphere within the chamber.

[0105] Even in any case, according to the X-ray diffraction (XRD: X-RayDiffraction), the protective film has (111) orientation. It has beenwidely known that (111) orientation is the orientation of the MgO singlecrystal, and has the great second electron emission coefficient and theexcellent sputtering resistance. Accordingly, the film having (111)orientation is suitable for the protective film of the PDP.

[0106] Further, in order to obtain the partial pressure ratio ofhydrogen and oxygen of 0.3 to 1, the partial pressure ratio may becontrolled with introducing oxygen gas and vapor or hydrogen gas intothe chamber. In case of introducing the vapor, because the vapor isdissociated into hydrogen and oxygen by the plasma produced by theelectron beam, it becomes possible to control the partial pressureratio.

[0107] Further, when forming the protective film, the parts such as acarrier to convey the substrate between the inside and the outside ofthe film forming apparatus are used. A MgO film having, for example, 0.1to 1 mm in thickness may be previously formed on the surface of theparts. Since the MgO film formed on the parts absorbs water when it issent to outside of the chamber, when the MgO film comes into the chambertogether with the substrate thereafter, it can disperse vapor in theinside of the chamber. Accordingly, with inflow of the oxygen gas fromthe outside, the partial pressure ratio of hydrogen and oxygen in thechamber can be controlled.

What is claimed is:
 1. A protective film protecting a dielectric layerof a plasma display panel from discharge, containing metallic oxide, anda volume resistivity of said protective film being 3.5×10¹¹ Ω·cm ormore.
 2. The protective film according to claim 1, containing 3 hydrogenatoms or more when the number of total atoms in said protective film isdefined as
 100. 3. A protective film protecting a dielectric layer of aplasma display panel from discharge, containing metallic oxide andhydrogen, the number of hydrogen atoms being 3 or more when the numberof total atoms in said protective film is defined as
 100. 4. Theprotective film according to claim 1, wherein said metallic oxide isMgO.
 5. The protective film according to claim 3, wherein said metallicoxide is MgO.
 6. The protective film according to claim 4, wherein apeak of light emission intensity of light emitting center in 510 to 560nm in a cathode luminescence is higher than that of light emissionintensity of light emitting center in 280 to 440 nm or 680 to 760 nm. 7.The protective film according to claim 5, wherein a peak of lightemission intensity of light emitting center in 510 to 560 nm in acathode luminescence is higher than that of light emission intensity oflight emitting center in 280 to 440 nm or 680 to 760 nm.
 8. Theprotective film according to claim 6, wherein the number of saidhydrogen atoms is at least the number of total deficits of total oxygenatoms and metal atoms.
 9. The protective film according to claim 7,wherein the number of said hydrogen atoms is at least the number oftotal deficits of total oxygen atoms and metal atoms.
 10. The protectivefilm according to claim 1, wherein said protective film is formed bymeans of performing a heat treatment in atmosphere including hydrogen inexcited or ionized state.
 11. The protective film according to claim 3,wherein said protective film is formed by means of performing a heattreatment in atmosphere including hydrogen in excited or ionized state.12. The protective film according to claim 1, wherein a surfaceroughness Ra of said protective film is 5 nm or more.
 13. The protectivefilm according to claim 3, wherein a surface roughness Ra of saidprotective film is 5 nm or more.
 14. The protective film according toclaim 1, wherein said protective film has (111) orientation.
 15. Theprotective film according to claim 3, wherein said protective film has(111) orientation.
 16. A method of forming a protective film protectinga dielectric layer of a plasma display panel from discharge, comprisingthe steps of: forming a metallic oxide film; and performing a heattreatment of said metallic oxide film in atmosphere including hydrogenin excited or ionized state.
 17. A method of forming a protective filmprotecting a dielectric layer of a plasma display panel from discharge,comprising the step of: forming a film containing a metallic oxide whileperforming a heat treatment in atmosphere including hydrogen in excitedor ionized state.
 18. A plasma display panel, comprising a protectivefilm according to claim
 1. 19. A plasma display panel, comprising aprotective film according to claim
 3. 20. A method of manufacturing aplasma display panel, comprising the step of: forming a protective filmby the method according to claim
 16. 21. A method of manufacturing aplasma display panel, comprising the step of: forming a protective filmby the method according to claim 17.